The presence of either synthetic or natural chemicals, poisons and toxins in soil, food, water and air can potentially effect human health. Substances to which people may be exposed include heavy metals such as arsenic, cadmium or lead; pesticides such as DDT or chlorpyrifos; industrial chemicals or wastes such as dioxins and PCB's and natural substances such as toxins from algae or fish.
Toxicology is a key tool used to assess perceived and actual health risks to humans from chemicals.